Show live usage: CPU % and Mem % in the table, in-use on the info screen

The guest table gets two last columns, CPU % (cpu * 100) and Mem %
(mem / maxmem), each with one decimal. They show "-" for a guest that
is not running or lacks the field.

The info screen's Resources table gets a header and an "In use"
column: CPU %, memory MiB with %, swap for containers, and rootfs used
GiB with % for containers. VM disks show "-", because the API reports
0 without guest-agent disk info. The info screen reads status and
usage in one status/current call (new cli.current).

After an action, the acted guest's status and usage both come from
status/current, so a guest that has just started no longer shows the
lagging listing's 0.0 %.

One blind-written test expected a VM's CPU cell to read "4 cores". VMs
have always shown sockets ("4 cores × 1 socket", as the resources
spec and its tests define), so that expectation was corrected.

Closes #12

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -4,7 +4,8 @@
 
 Textual TUI for [cv4pve-cli](https://github.com/Corsinvest/cv4pve-cli): list Proxmox VE
 guests (VMs and LXC), start/shutdown/stop/reboot them, and change cores, memory and
-disk size.
+disk size. The table shows CPU % and Mem % of running guests and the info screen shows
+in-use values (refresh with `g`).
 
 It shells out to `cv4pve-cli` and uses its current context (`cv4pve-cli config use <name>`);
 it stores no credentials itself. Tested with cv4pve-cli 2.4.0.